1. Field of the Invention
The present invention relates generally to an airfoil in a turbo machine, and more specifically to the process for designing an airfoil using computational fluid dynamics analysis.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A turbo machine includes one or more rows of airfoils, such as rotor blades and stator vanes that compress or expand a fluid due to the rotation of the airfoils. A compressor for an aero gas turbine engine includes several rows of rotor blades and stator vanes that progressively compress the air to high pressures. For example, the Pratt & Whitney JT8D turbofan engine used to power the Boeing 727 and 737 aircraft has a compressor with 11 stages with a compression ratio of 17 to 1.
The engine efficiency can be increased by improving the compression ratio of the compressor. The design process for the compressor includes complex computer analysis that includes a CFD (computational fluid dynamics) study of the airflow through the row or rows of vanes and blades. Through this CFD analysis, the design engineer can improve on the airfoil shapes so that the performance of the airfoils can be maximized.
In the prior art, the CFD analysis of a turbo machine blade row that is used in a turbo machine like a compressor and in which the blades are not cooled by passing cooling air through the interior of the airfoil, a number of variables are input to the analysis and a number of variables are output by the analysis. The properties of the fluid (such as air) is input variables and include the pressure P of the fluid, the momentum M of the fluid in each of the X, Y and Z axis, and the temperature T of the fluid that enters the airfoil. Also input variables include the momentum of the wall in each of the X, Y and Z axis. The back pressure P of the airfoil is also inputted into the analysis and is a constant with a predefined value. These are the input values for the analysis. The CFD analysis of the prior art is an adiabatic process since no heat transfer flows to or from the airfoil.
The output variables for the analysis include the wall Pressure and the wall Temperature, and the fluid momentum in the X, Y and Z axis, temperature of the fluid flow at the outlet of the airfoil, and the wall temperature. In this prior art CFD analysis, the wall Temperature is calculated in the analysis. Thus, the prior art analysis includes 9 inputs and 6 outputs that include the Wall Temperature of the airfoil. This analysis requires long periods of time to calculate, especially since the wall temperature of the airfoil is one of the 6 output variables that must be calculated in the CFD analysis. Convergence of CFD solutions consumes massive amounts of computational resources and designer time. Any method to reduce the time per simulation increases the number of simulations in a design cycle and leads to quicker and better designs of the turbo machine. In another prior art analysis, the wall temperature of the airfoil is guessed at and is therefore set before the CFD analysis is performed.